The publication US 2010/0244651 A1 discusses a previously known spark plug, in which the ground electrode is welded on both sides to the front side of the housing in the form of a bridge. Because of the two opposite weld points, this ground electrode is subjected to high thermal stresses, which are in particular caused by the different thermal expansion coefficients of the electrode material and the housing material. In addition, with the bridge-shaped ground electrode, it is not possible to subsequently adjust the gap between the center electrode and the ground electrode by bending the ground electrode.
Publication DE 101 55 404 A1 discusses a spark plug according to the definition of the general species of spark plug. Here, the housing having the thread is very deeply recessed with respect to the combustion chamber end of the center electrode. Consequently, the ground electrode includes a very long component extending parallel to the center axis of the spark plug. This configuration has two decisive disadvantages: The relatively large and long ground electrode constitutes a relatively large surface for absorbing the heat in the combustion chamber. Relative to this very large heat-absorbing surface, the previously known ground electrode has only a very small cross section at the connection point between the ground electrode and the housing. Only this very small cross-sectional area may be used for dissipating heat from the ground electrode into the housing. This unfavorable relationship between the heat-absorbing surface and the heat-dissipating cross section causes substantial thermal stress of this previously known ground electrode, thus resulting in increased oxidation and a shorter lifetime. In addition, this configuration has substantial disadvantages when adjusting the gap between the center electrode and the ground electrode. To adjust this gap, the ground electrode must be bent toward the center electrode after connection to the housing. The previously known ground electrode has a very long component parallel to the center axis of the spark plug. When bending the portion of the ground electrode opposite the center electrode, an unfavorable bending moment acts on the portion of the ground electrode parallel to the center axis. Adjustment of the gap is thus not optimally possible in the previously known arrangement.